What is a Transmission Solenoid?
The transmission solenoid is a type of electromechanical valve that controls the flow of fluid. Specifically, in an automatic transmission, we mean the flow of automatic transmission fluid into and through the transmission.
In modern transmissions, the transmission solenoid generally comes in a pack which is installed in the transmission control unit, the transmission control module, or a transmission valve body.
Transmission fluid is critical to the function of the transmission. If its flow is impeded or hindered, your transmission cannot operate properly.
The Role of Transmission Solenoids in Smooth Shifting
Regulating Transmission Fluid and Pressure
In addition to controlling gear changes, transmission solenoids also play a crucial role in regulating the pressure and flow of transmission fluid throughout the transmission system.
This is essential for maintaining proper lubrication and cooling of the transmission components, as well as ensuring that the clutches and bands engage and disengage at the right times.
The Consequences of Malfunctioning Solenoids
Without properly functioning solenoids, the transmission may experience issues such as delayed or harsh shifts, slipping gears, or even complete transmission failure.
This highlights the importance of ensuring that transmission solenoids are functioning correctly to prevent these problems from occurring.
The Importance of Transmission Solenoids
In conclusion, transmission solenoids are integral to the overall performance and longevity of an automatic transmission.
Their proper functioning is essential for ensuring smooth gear shifts, maintaining transmission health, and preventing costly repairs.
How Does a Transmission Solenoid Work?
As you drive down the street, the car’s computer analyzes data sent from vehicle speed sensors and engine speed sensors. Based on this information, the engine control module (ECU) or the transmission control module (TCM) performs the appropriate upshift/downshift by sending a signal to one of several shift solenoids.
These transmission solenoids have a spring-loaded plunger inside that is wrapped with wire. When this coil of wire receives an electrical charge from the TCM / ECU, the plunger opens allowing transmission oil to flow into the valve body and pressurize the desired clutches and bands. In this case, the transmission changes gears and you will drive down the road.
The car’s computer can control the transmission solenoid in a number of ways. If the vehicle is equipped with a special transmission control unit, it can open or close the hydraulic circuit with a direct 12 V signal.
Or the engine control unit can control the solenoid’s plunger by turning the ground circuit on and off. A solenoid can be used to control a single gear or multiple gears, depending on the complexity of the design.
Symptoms of a Bad Transmission Shift Solenoid
When a shift solenoid starts to misbehave, your transmission won’t be shy about letting you know. The symptoms can range from annoying quirks to serious issues that leave you stranded. Here are the most common red flags to watch for:
#1. Delayed Gear Engagement.
Ever shifted into drive or reverse and felt like your car was thinking about it for a moment too long? That’s a classic sign of a bad shift solenoid. The hydraulic fluid isn’t getting to where it needs to go quickly enough, leaving you waiting and wondering.
#2. Stuck in One Gear.
If your car suddenly decides it’s happy staying in first gear—or worse, it won’t come out of neutral—you’re likely dealing with a failed solenoid. It’s like the transmission has lost its ability to switch gears entirely.
#3. Erratic or Harsh Shifting.
Does your car lurch forward like it’s got something to prove every time it shifts? Or maybe the shifts are so jerky, you feel like you’re in a go-kart. Either way, inconsistent or rough shifting is a telltale sign your solenoid isn’t playing ball.
#4. Gear Slippage.
You’re cruising along, and suddenly, the transmission slips out of gear, leaving you revving and going nowhere. Not only is it annoying, but it’s also dangerous—especially in traffic. https://imasdk.googleapis.com/js/core/bridge3.686.0_en.html#fid=goog_579499081
#5. Check Engine Light.
Ah, the dreaded dash disco. A faulty shift solenoid often triggers the check engine light, especially in modern cars. Grab an OBD-II scanner, and you’ll likely see a transmission-related code pointing to the solenoid.
Here’s the common ones – P0750, P0751, P0752, P0755, P0756, P0757, P0760, P0761, P0762, P076, P0770.
#6. Poor Fuel Economy.
A bad solenoid can throw your transmission’s timing off, making the engine work harder than it should. The result? You’re burning more gas than usual—and feeling the pinch at the pump.
#7. Transmission Overheating.
Struggling to shift properly means your transmission has to work overtime. That can lead to overheating, which is a slippery slope toward more costly repairs if ignored.
If you’ve noticed any of these symptoms, it’s time to take action. Ignoring a failing shift solenoid won’t just make your drive unpleasant—it can lead to bigger, spendier problems down the road. Catch it early, and you’ll save yourself a lot of hassle and cash.ift solenoids).
How to Diagnose and Replace a Faulty Transmission Solenoid
Diagnosing and replacing a faulty transmission solenoid is complicated, so it’s best to have a mechanic handle it.
To diagnose a transmission solenoid problem, they’ll:
- Read the diagnostic code: They’ll connect an OBD-II scanner and read the problem codes associated with different transmission parts.
- Check for common symptoms: Gear issues and transmission fluid leaks are telltale signs of a faulty solenoid.
- Test the solenoids: They’ll use a multimeter to test the electrical resistance of each solenoid coil (around 10 ohms, depending on the solenoid coil). They might also apply air pressure to determine if the solenoid valve opens and closes properly.
Once they’ve diagnosed the faulty transmission solenoid, they’ll replace it:
Step 1. Disconnect the Car Battery
The mechanic will remove the negative and positive battery terminals, respectively. They’ll also remove the dipstick from the transaxle to access the solenoid easily.
Step 2. Loosen the Fill Plug
Before draining the transmission fluid, they’ll loosen the fill plug to prevent it from getting stuck. This makes it easier to refill the pan later.
Step 3. Remove the Fluid Compartment
The mechanic will unscrew each bolt that secures the fluid compartment to the bottom of the transmission and remove the gasket from the transmission pan.
Step 4. Drain the Transmission Pan
Before draining the pan, they’ll place a container underneath the transmission to catch the fluid and remove the drain plug.
Step 5. Unscrew Fix Plate Bolts
They’ll locate the solenoid, disconnect all wires from the unit, and remove it from the fixing plate (the mounting surface where the solenoid is attached).
Step 6. Replace the Valve Body and Solenoid
The mechanic will turn the locking ring to release the fill plug from the valve. Afterward, they’ll remove the sleeve and each bolt attaching the valve body to the transmission.
They’ll pull the wires and pry the solenoid from the housing mount, replacing it with a new one.
Step 7. Reassemble the Components and Add Fluid
They’ll refill the transmission fluid and reattach all other components.
Now that you know about transmission solenoid replacement, read on to discover the costs.
How Much Does a Transmission Solenoid Replacement Cost?
You’ll pay around $250 to replace a transmission solenoid (including labor). If you need to replace a solenoid pack, the cost could reach $600.
The cost depends on your vehicle’s make and model, as well as the mechanic’s labor rate. For instance, a solenoid pack on a BMW will be more expensive than on a Honda Motor Company vehicle. Additionally, the complexity of the transmission system may lengthen the labor time.